The present invention relates generally to gasification power systems, such as those used in a power plant, and more specifically, to gasifiers used in integrated gasification combined cycle (IGCC) power systems.
At least some known combined cycle power systems include a gasification system that is integrated with at least one power-producing turbine system. For example, known gasifiers convert a mixture of fuel, air or oxygen, steam, and/or limestone into an output of partially combusted gas, sometimes referred to as “syngas”. The hot syngas is cooled and cleaned to remove contaminants and then supplied to the combustor of a gas turbine engine, which powers a generator that supplies electrical power to a power grid. Exhaust from at least some known gas turbine engines is supplied to a heat recovery steam generator that heats boiler feed water and generates steam for driving a steam turbine. Power generated by the steam turbine also drives an electrical generator that provides electrical power to the power grid.
In at least some gasifiers used in gasification systems, the syngas that is generated in the reaction chamber is very hot (>2200° F.) and must be cooled before it can be handled easily in downstream process equipment. The syngas also contains entrained particles which must be removed to prevent plugging in downstream equipment. For power generation applications, at least some known gasifiers accomplish this cooling and particle removal using a two-step process. In the first step, the gas is cooled by indirect heat exchange with boiler feed water in two syngas coolers. The first syngas cooler, called a radiant syngas cooler, is coupled to the bottom of the reaction chamber, and it cools the gas to between approximately 950° F. and approximately 1350° F. The second syngas cooler, called a convective syngas cooler, further cools the gas to between approximately 700° F. and approximately 750° F. At such temperatures, the syngas may be handled in conventional steel equipment. After cooling the syngas using the syngas coolers, the second step, removing the fine particulates entrained in the syngas, is accomplished in another vessel called a syngas scrubber. The syngas scrubber provides three stages of water-syngas contact, which remove virtually all of the particulates.
In at least some combined cycle power applications, the convective syngas cooler is removed from the system leaving only a radiant syngas cooler to cool the syngas. This so-called radiant-only configuration is used in at least some combined cycle applications for two reasons. First, removal of the convective syngas cooler reduces the cost of the plant. Second, in commercial practice, the convective syngas cooler has been found to be prone to plugging, which significantly reduces plant on-stream time. But, removal of the convective syngas cooler presents two problems. First, the approximately 950-1350° F. temperature at the exit of the radiant syngas cooler is still too high to allow the syngas to be handled in conventional steel piping and equipment. Second, at that temperature, some of the entrained solids are still sticky, and they can plug the piping connecting the radiant syngas cooler to the syngas scrubber. As such, removing the convective syngas cooler to create a radiant-only syngas cooling configuration is not a simple matter of removing the convective syngas cooler and connecting the scrubber directly to the outlet of the radiant syngas cooler. To do so would require, at a minimum, the scrubber vessel to be manufactured from special high temperature steel alloys and would invite the possibility of solids plugging within the scrubber vessel itself. An apparatus is needed to cool the syngas by quenching with water sprays and to remove entrained particles while avoiding concerns about plugging. Moreover, an apparatus is needed to simplify the equipment required for syngas cooling and particle removal by eliminating the need for a separate syngas scrubber vessel.